Methods: All subjects were bitten under laboratory conditions by Aedes aegypti mosquitoes at one spot on the ventral aspect of the left forearm and another on a corresponding position on the right forearm. One spot was treated with the homeopathic after-bite gel and the other with a placebo gel.

Main outcome measures: Itching was assessed on a 5-point discrete rating scale at 0, 0.5, 1, 26.5, and 48 h post-bite to compare the itch-relieving efficacy of the two treatments. Erythema development was assessed by photographing the bite sites, measuring length and width of the erythema with at baseline (T0) to the mean erythema surface at 0.5, 1, 26.5, and 48 h post-bite (Tmean) for the two treatments.

Results: Testing erythema development by comparing the ratio T0/Tmean, after-bite gel and the ratio T0/Tmean, placebo gel gave a two-tailed p=0.098 (95% Cl,−0.031–0.361) in favour of the after-bite gel. There was not a statistically significant difference between the itch relief provided by the two treatments (two-tailed p=0.424; 95% Cl,−0.541–0.191). The correlation between itching and erythema was significant (r=0.46; p<0.001).

Conclusions: There are strong indications that the homeopathic after-bite gel reduces erythema development following mosquito bites. The homeopathic mother tinctures of Echinacea angustifolia DC., Ledum palustre L, Urtica urens L. as well as the Hamamelis extract in this gel, whether alone or in combination, are the biologically active ingredients. The homeopathic after-bite gel was not demonstrated to relieve itching, however, based on the correlation between erythema and itching, an effect on itching is not inconceivable.